Despite our extensive catalogue, we understand that every lab has specialty needs that only a skilled scientific glassblower can tackle. To support those efforts, we’ve assembled a broad range of glassblowing supplies. Scientific glassblowers can choose from our selection of flanges, blanks for lids and vessels, stirrer shafts, bearings, and other essentials for manufacturing customer-specific pilot plants, bioreactors, wiped film evaporators, or distillation apparatus. In addition to our portfolio of laboratory articles, our glassblowing supplies include blanks for further processing; for example, when a master glassblower requires separating or dropping funnels and evaporating flasks. Each product group offers the opportunity to work without grease.

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Supporting Scientific Glassblowers

Most laboratory glass apparatus consists of several components. And at some point, pumps, thermostats, thermometers, and measuring electrodes all have to be connected. We understand that those connections are not to be taken lightly and, in fact, must adhere to safety, tightness, chemical, thermal and mechanical resistance requirements. That’s why we’ve compiled a range of connectors to help you fulfill the various and specific needs of your customers. Because we know that certain instances demand that you work without grease, each product group has grease-free options. In addition to offering components for connection, our glassblowing supplies also include closures and accessories for securing connections.

Regulating the flow of gas or liquid is one of the main functions of laboratory equipment
— whether it’s a simple separating funnel or a complex Schlenk lines for the high
vacuum range. Choosing the right components is vital for ensuring the flawless function
of the final product made by the scientific glassblower. Here’s a quick guide to help you
make the right choice:
Dosing function -> Valve
HV range -> PRODURAN®
Budget -> GU-Valve
Open and close -> Single way stopcock
Budget -> massive plug
Free of grease -> PTFE-key
Temperature change-> Hollow plug
Vacuum -> Taper 1:5
Schlenk line -> 2 Way Stopcock
Special applications -> 3 Way Stopcock
For greaseless applications in processes involving temperature changes, stopcocks
with PTFE plugs are not the first choice. PTFE has a much higher thermal expansion
when compared with DURAN®, so temperature changes may lead to decreasing

tightness. In such cases, the glassblowing supply we recommend are spindle valves
(PRODURAN®, GU-Valves).

Our filter discs are made of DURAN® glass to ensure that no additional stress occurs when a filter is fused to a DURAN® tube. Permanent stress inevitably results from deviating material properties such as the coefficient of thermal expansion (α) and the transformation temperature (Tg), increasing the demands of an already challenging
working process.

The pore size of sintered glass filters is controlled by the grain size of the glass powder used, and of course, by the settings of the sintering process. Here at DWK Life Sciences, the pore size and the mechanical strength of the frits are subject to strict quality control. You’ll find helpful diagrams regarding the flow rates for fluids and gas, as well as further technical information here.

The off-the-shelf product line of DWK Life Sciences laboratory glassware offerings —
flasks, beakers, and separating funnels — is extensive and meets the needs of many standard applications. But we’re well aware that in many cases, the customer’s needs require custom-built products. That’s why, in addition to our catalogue laboratory articles, we offer blanks for further processing by scientific glassblowers, for example for separating or dropping funnels and evaporating flasks. You can depend on the consistently uniform wall thickness crucial for your success; we know that deviation of
the wall thickness increases thermal stress in the glass, resulting in a higher risk of
breakage.

Reaction vessels and plants are generally constructed according to the customer’s needs. And while DWK Life Sciences most often supplies products to the end user, we recognize that there’s also demand for tailored solutions to the final customer. That’s where scientific glassblowers step in, using our wide range of flanges, blanks, stirrer
shafts, bearings, and other accessories to manufacture customer-specific pieces like pilot plants, bioreactors, wiped film evaporators, and distillation apparatus.

DWK Life Sciences offers a comprehensive range of volumetrics. Pipettes, burettes, mixing and measuring cylinders, as well as measuring flasks are all available in various sizes, models, and accuracy classes. As with our other segments, blanks are also a part of this offering. Our catalogue includes unprinted, ungraduated items for the manufacture of customized volumetric products. The tight tolerances of the semi-finished products are achieved by using high-quality raw material, for example, DURAN® tubes with limited tolerance range. This facilitates subsequent processing alongside of reduced cost.

Frequently Asked Questions

It’s important to note that roughness cannot be defined by the grain size used in the grinding process. Parameters like the rotational speed, the grinding fluid used, and the contact pressure have an impact on the resulting surface properties. For this reason, the requirements to the surface quality according to international standards and to our specification refer to the arithmetical roughness of the surface (Ra). DWK Life Sciences uses various methods for grinding — including diamond tools, silicon carbide, manual operations as well as fully automated processes, depending on the type of product, the lot size and the requirements.

First a word of caution: broken glass is sharp edged and there is always a risk of injuries, even for experts. The favorable method to disconnect wedged joints requires three hands, so please ask a colleague for help. Carefully pull the cone and the socket apart — no excessive force as the glass may break at any time. While pulling, ask your colleague to shatter the joint by tapping on one of the tubes beside the connection. Use something similar to a ballpeen, made of wood or plastic — not metal — and be very cautious. If possible, turn the connection and tap from all sides. If there is no space to tap on one of the tubes, consider tapping on the joint. In this case, you have to be even more careful. Do not increase the force, when the joints do not disconnect. Successfully separating a frozen joint is a matter of finesse, not strength. Take a look at the question and answer below to learn how to avoid this situation going forward.

  • Always use either vacuum grease or PTFE sleeves
  • When the apparatus is not in use, all joints should be disconnected
  • Never put a cold cone in a hot socket
  • When working with fat solvent, make sure that the joints stay lubricated
  • Keep in mind, wet joints tend to stick, particularly when wetted by alkaline solutions

The truth is that nothing is 100% tight. Everything has a leakage rate, even an incandescent lamp or a neon tube. The effective leakage rate of ground joints and stopcocks depends on a number of factors. In addition to the properties of the cone and the socket, like the roughness of the joints, the accuracy of the taper, and the roundness, proper handling factors greatly in practical tightness. Appropriate usage of
vacuum grease and the correct use of the retaining device are essential for achieving a
minor leakage rate. For these reasons, the DIN-standard 12 256 (tightness test of conical joints and stopcocks) refers to unlubricated joints to make measurements comparable. The requirement to the leakage rate according to DIN 12 540 and 12 541 is this: ≤ 0,1 mbar l/s -1 . This is obviously not a high-level value, and the leakage rate of lubricated stopcocks is better by orders of magnitude. However, for the reasons stated above, it is not possible to give a universally valid specification of the leakage rate of lubricated stopcocks. Generally, we recommend using valves for requirements to the leakage rate ≤ 10 -3 mbar l/s -1 . For PRODURAN® valves, we guarantee a leakage rate ≤ 10 -6 mbar l/s -1.

KECK TM clips — which ensure a safe connection — are available for conical and for spherical joints and are easy to attach and to loosen. For even stronger connections, DWK Life Sciences recommends using Safety Joints. This type of connection offers a much higher retention force and additionally provides a system to release “frozen” joints.

Attention: Please consider, that in contrary to KECK TM clips, Safety Joints will not release overpressure. When using Safety Joints, you have to make sure that your apparatus is either resistant to pressure or that a pressure relief valve is implemented.

Sizes of ground joints are generally specified by two numbers, separated by a slash.
The first number stands for the largest diameter (mm) of the ground area. For many
sizes, the nominal size is a shortcut for the real size, like NS 19 (stands for 18,8mm) or
NS 29 (29,2mm). The second number stands for the projection of length of the ground
zone.
Example: NS 14 / 23
largest diameter (d): 14,5 mm
length (l): 23,0 mm
taper: 1:10
smallest diameter 14,5 – 23/10 = 12,2 mm