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Solar thermal adheSiveS

Forming bondsAdhesives are becoming increasingly important

in collector production.

SUN & WIND ENERGY explains whyand introduces adhesives providers.

Adhesives are suitable or bonding pieces to-

gether. This year, more than ever, adhesives

manuacturers have sought to orm bonds

with solar thermal companies. In May, Dow Corning

GmbH o Wiesbaden and Kmmerling Chemische

Fabrik GmbH o Pirmasens two frms with long years

o experience in adhesives applications made their

frst appearance at the OTTI Symposium in Bad Sta-

elstein, Germany. In June, Tremco illbruck GmbH &

Co. o Cologne rented its frst-ever stand at Intersolar

Europe in Munich. In solar thermal Hall B1, the com-

pany presented its Pactan-brand adhesive sealants.

In 2009, the company began adapting these adhe-

sives to collector production.

Our single component adhesive sealants have a

broad adhesive spectrum and are suitable or bond-

ing a collectors glass to its rame or to bond the back

wall o the collector. They bond quickly and can with-

stand temperatures o up to 160 C, says Key Ac-

count Manager Volker Scheidler, explaining the prop-

erties o the solar thermal adhesives. By contrast, thefrms two-component solar silicones are character-

ised by short curing times, enabling throughput rates

o less than 90 seconds, according to Scheidler. He

Bonded joints do not

require mechanical pro-

tection and thereore do

not need a covering rail.

Graphic: Tremco Illbruck

The bonding eect

between the adhesive

and the rame allows or

new designs.

said that the adhesives eliminated the need or ex-

pensive curing lines. Within just a ew minutes, ac-

cording to Scheidler, the collectors can be stacked on

pallets.

Collector manufacturers preferadhesive technology

More and more collector manuacturers in the Ger-

man-speaking region are producing bonded collec-

tors, according to a market survey by SUN & WIND

ENERGY. According to the survey, adhesive technolo-

gy has established itsel as the most requently used

method o attaching the sides o collectors with

rames. As recently as 2008, collector manuacturers

still preerred mechanical shaping techniques, such

as clinching. Adhesive processes now dominate, even

or attaching glass covers. While three years ago

62 % o all solar collectors sold in Germany were

sealed around their edges with an EPDM seal and had

glass covers clamped on with rails, now more thanhal o all solar collectors have glass covers bonded

to their rames with adhesive, which also keeps out

moisture.

The transition to new joining techniques is no

accident. Compared with mechanical joining sys-

tems, automation with liquid adhesives is simpler

and easier, says Sebastian Terner, explaining why

adhesives are increasingly being used in automated

collector production. The sales proessional works

at sealant and adhesives manuacturer Hermann

Otto GmbH in Fridolfng, Germany. The company has

been supplying adhesives to collector manuactur-

ers or ten years. This year, the frm intensifed its

marketing eorts and produced a brochure in

English called High-quality connections or solar

collectors, which provides an overview o its solar

thermal adhesives. The companys product line in-

cludes silicones or bonding glass plates and a poly-

urethane or bonding plastic caps to the corners o

collectors.

Adhesives enableslim collector designs

In addition to their suitability or automation, bondedconnections also have other benefts. Unlike a dry

seal with a clamp rail, joining with an adhesive gives

you a proper bond. This bonding eect opens up

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completely dierent structural possibilities or collec-

tor manuacturers. They can make collectors really

slim because, o course, the glass also contributes to

the stability o the joint, explains Dow Corning Mar-keting Manager Markus Plettau. The elastic bond with

highly adhesive silicone creates a joint between the

glass and the rame along the entire perimeter which

absorbs and compensates or movement, preventing

penetration by air and water. Mechanical astenings

or the glass are generally unnecessary.

Dow Corning transerred its knowledge rom the

area o bonded aade construction to solar thermal

more than 15 years ago. No mechanical cover is

needed in addition to the slim, bonded joint which

enables maximum use o the glass absorber surace.

This can oer cost benefts, in addition to aesthetics

and perormance. In short, this structural adhesive

technology enables innovative, hard wearing, and

delicate construction, the company wrote in its por-

trait in the OTTI association conerence proceedings.

The bonded collectors just look great, says Plettau

in an interview.

Silicone adhesives are optimally suited to the de-

mands o solar collectors. Silicones belong to the

synthetic polymers group, in which silicone atoms

are bonded together via oxygen atoms. The inorgan-

ic latticework, with its organic components creates

Polyurethane is used or

bonding plastic caps to

the corners o collectors.

Photos (4): Otto Chemie

SMEThermal conference: focus on production

Those who would like to fnd out more about the advantages and disadvantag-

es o adhesives and discuss them with other experts rom the industry will be

provided with the opportunity to do so at the international SMEThermal coner-

ence, the only event that ocuses on solar thermal production technology. Addi-

tional ocus areas include:

potential for cutting costs throughout the entire value added chain,

the implementation of the Eco Design directive in the industry,

quality of metal and glass coatings,

global collector certication and

design and production of polymer storage tanks.The event will take place on 7th February 2012 in Berlin, Germany. The coner-

ence, which is being organised by SUN & WIND ENERGY in conjunction with So-

larpraxis AG rom Berlin, will be held in English.

Further information: www.solarpraxis.de/en/conferences/smethermal-2012

http://www.novasol.es/

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Solar thermal adheSiveS

A robot bonds the back

wall o a collector at the

frm Citrin in Moosburg,

Germany.Photo: Joachim Berner

Pull-o testing

equipment tests

adhesion.

Photo: Sika Services AG

properties which beneft the solar thermal industry.

Their structure enables them to resist both UV radia-

tion and weathering. They hold their bond at low andhigh temperatures. Their high elasticity enables them

to bond dierent materials together and compensate

or their dierent coefcients o expansion. In short,

they bond best to glass, aluminium and steel, all ma-

terials that collector manuacturers use or the cover,

rame components, and back wall.

Adhesive types and differentcuring times

The properties o silicones have to suit the process

speed o collector manuacturers, which is why most

adhesives manuacturers oer both one-part and

two-part systems in their product ranges. One-part

adhesives consist o a single component and require

moisture rom the air in order to cure. Thereore, the

time it takes or them to cure is dependent on exter-

nal climate conditions. Depending on the depth o

the joint, curing can take up to a day. One-part adhe-

sives are well suited to manual production steps

because they can be applied by hand without great

haste.

The two-part products work aster. They comprise

an adhesive and a curing agent, which accelerates

the process. The two-part adhesives make manuac-turers independent o the climate in their production

halls because the adhesives do not need moisture

rom the air to polymerize. The reaction begins as

soon as their two components are mixed. With two-

component adhesives, the pot lie the handling

time in which the mixture can be used can be ad-

justed in a range, rom hal an hour to just a ew min-

utes, enabling adaptation to semi- or ully automated

production processes.

No adhesion without adaptation

and controlsAdjusting the curing time requires a good bit o spe-

cialised knowledge. Most adhesives manuacturers

thereore oer not only drums and tanks o adhe-

sives; they also provide advice to their clients. For in-

stance, Dow Corning perorms adhesion and compat-

ibility tests or various substrates on request. Provid-

ers also oer their customers support in the construc-

tion and testing o collector designs or in calculating

joint dimensions, based on anticipated tempera-

tures, as well as dynamic and static loads. The mix-

ture o adhesive and process is key. Adapting auto-

mation and dosing equipment to the adhesive and

customer is very important, says Hermann Otto em-

ployee Terner.

However, adapting the adhesive to the collector

design, joint geometry, and manuacturing process is

not enough to ensure that the glass plate stays glued

to the collector rame. Dow Corning manager Plettau

underscores the importance o constant production

monitoring, Even i collector manuacturers ultimate-

ly have the process under control, they have to keep

one very essential point in mind: quality assurance in

the application o the adhesive, he says.

The international adhesives producer Sika AGrecommends that its customers perorm running

tests to check both the quality o the adhesive mix-

ture and that o the bonded products. For instance,

the company advises collector manuacturers using

two-part adhesives to check the mixture ratio o the

two components coming out o the dosing unit every

day beore they start production or when changing a

drum. Also, the two components have to mix as ho-

mogeneously as possible in order to provide opti-

mum adhesion. Sika also recommends a special test

or just that purpose. Finally, various pull-o tests can

be used to determine adhesion that is, both the

strength o the bond and its adhesive orce which is

particularly recommended or bonds with complex

geometries. Such testing shows whether the adhe-

sive flls the entire joint.

Checking the adhesive takes on even greater im-

portance i something changes in the manuacturing

process. The main issue is when a collector manu-

acturer changes a material or material supplier, or al-

ters the manuacturing process in some way. What

can happen then is that the bonding process might

stop working properly, says Tremco illbruck manag-

er Scheidler. His companys products oer process

security because the A-components are made to besel-hardening. That ensures that the adhesive works,

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even i the dosing ratio o the two adhesive compo-

nents is o by a bit.

Filling joints uniformly

Adhesives development continues. Some manuac-

turers are developing so-called sel-leveling adhe-

sives. They can fll the joints o a solar collector even-

ly, even i its geometry deviates rom the desired val-

ue due to unevenness o the material. In such cases,

automatic bonding techniques using standard prod-

ucts could apply either too little or too much adhesive

to the joint. Too little adhesive can produce a visual

ault and require excessive fnishing work. Workers

have to remove excess adhesive by hand.

Kmmerling oers the solar thermal industry a

bonding agent it has never had beore, butyl adhe-

sive. I a collector is permanently flled with gas, a

silicone sealant is inadequate. To meet this more de-manding requirement, additional measures are need-

ed to seal the collector, says Product Manager Frank

Simon. That is why Kmmerling made its butyls or

solar collector edge seals gas and water tight and

heat resistant to temperatures in excess o 100 C.

Furthermore, we added an agent which chemically

bonds to the glass, which means that even i the ad-

hesives get a bit sot or are moved by the glass, they

remain intact.

Joachim Berner

Providers of silicones for collector production:

Dow Corning GmbH: www.dowcorning.comHenkel AG & Co. KGaA: www.henkel.com

Hermann Otto GmbH: www.otto-chemie.com

Kmmerling Chemische Fabrik GmbH: www.koe-chemie.de

Sika AG: www.sika.com

Tremco illbruck GmbH & Co. KG: www.tremco-illbruck.com

The right adhe-sive in the rightplace

Henkel AG & Co. KGaA

created a graphic to

illustrate where adhe-

sives can be used in so-

lar collectors. The red

indicates where adhe-

sives can be applied.

For instance, between the glass cover and the collector rame, on the corners o

the collector, or on the back wall. The Dsseldor adhesives manuacturer oers

products or each application.

Loctite silicone adhesives oer good protection or the glass cover against

weather eects or temperatures up to 180 C, or instance. With handling times

o up to three minutes and workability ater just fve minutes, they are well

suited to ast production processes.

The polyurethane adhesive Macroplast or corner joints has handling times

o 10 and 45 minutes and orms a stable bond ater some 40 minutes. It is tem-perature resistant rom -40 to 80 C, but Henkel also oers two other Loctite

products or the very high temperatures inside o collectors. The high-tempera-

ture products can withstand temperatures o up to 300 C, which means they

can be used to bond liquid-carrying tubes to an absorber plate.

http://www.solartech.com.my/