Overview of the types on needles and nozzles

Needle vs. Nozzle
Needles use surgical tubing or narrow (needle) passages, while a nozzle is a general term meaning needles and conical nozzles and other dispensing tips.


Materials

Plastic – disposable, these are the cheapest type of nozzles or needles. They are great for general use.  The disposable nature and quick disconnect are advantages. There are a few disadvantages, these include:

  1. Plastic will flex. It happens when the pressure inside the needle changes (like during a dispense.
  2. There is variation from needle to needle. This means the every needle change requires a machine adjustment
  3. It wears, particularly with filled materials like ceramic filled epoxies and silver filled epoxies, the material wears the needles out
  4. Plastic is not inert. Plastics can deteriorate or swell with different solvents and chemistries.

Stainless steel – Stainless is a huge step forward in eliminates many of the problems with plastic needles. They wear, but slower, they can flex, but very little, there is variation, but less, they are not inert, but they are generally not chemically susceptible.  There are 3 types:

1- Stainless steel Composite needles. These use surgical tubing and mount this tubing in a hub. The mounting can be glued in, or swedged in, or welded in. This is a much better than plastic. These needles can run days, or weeks, they can be cleaned, the dispense to dispense consistency is good. There are a few disadvantages, these include:
The surgical tube to hub interface often lacks uniformity. This means cleaning this area may not be possible, it also means the consistency is not complete. Wear is much less than the plastic, but wear ofte means the outlet diameter will increase with abrasive materials like silver epoxy.

2- Stainless steel Machined needles. These are one piece, the problems with the joining of a surgical tubing to a hub is elementated. The consisticy is improved, There are still a few disadvantages, these include:
Wear is much less than the plastic, but wear often means the outlet diameter will increase with abrasive materials like silver epoxy. Machining into a blind hole requires a talented machist. Even this means the smallest needles are difficult to make. These can be very expensive.

3- Ceramic needles. In many ways these are the ultimate nozzles. They are molded, and the molds are a reverse image of the inside of the nozzle. This allows the machinist to see the surfaces and make a prefect inside surface. It is consistence nozzle to nozzle, cheaper to produce because it is molded and the material (ceramic) is inert. Wear happens, but very slowly. There are still a few disadvantages, these include:
Lack of availability, there are few producers and certain shapes are difficult – like dual dot nozzles or multi port designs.


Needle and Conical Shapes

The history of needles comes from the medical industry. The medical uses are all for liquids that are low (like water), the pressures low, and the amounts comparably large. In mechanical and electronic assembly operations the liquids are normally higher viscosity, the shot sizes smaller and the pressures much higher. The flow dynamics internal to the needle is much more important. There are times when forcing a material down a long narrow passage (like a surgical tube) is required – for example dispensing into blind holes through RF shields or into deep cracks. Generally, a needle is not required, and a more open, optimized fluid path can be used. These are conical nozzles. There are a number of advantages to conical shapes Conical shapes clog less, wear less, require less pressure and because of these advantages can successfully dispense smaller dots.

Generally, needles are used for dispensing into limited access areas, and multiple port application. Conical nozzles are not used in dispensing into blind holes, or multiport applications, but other than these applications the conical nozzles are more advantageous. They can dispense smaller dots and lines, have less wear, and require less pressure. Less pressure means the seals and connections in valves are stressed less and require less cleaning.


Other Variations

Bent needles – angled for access into difficult areas or angled for reduced hand stess.

Length – shorter needles require less pressure, longer needles allow for access into limited spaces.


Connections

Lure Lock connection. This is a standard for fluid fittings. It is twist on connection that makes a leak free connection between a male tapered fitting (normally on the nozzle side) and a female fitting (Normally in the syringe). Lure is the name of the German inventor Hermann Wülfing Luer. There are 2 varieties of Luer connections: The Luer-Lok and Luer-Slip. Luer-Lok fittings are used in industrial dispensing. The Luer-Lok fitting was developed in the United States by Fairleigh Dickinson.

Camalot – The Camalot fitting is a round hub with a flat or a groove at a specific angle (0 or 90 degrees is common). It uses a threaded cap to connect it to the valve.

Twist – These can be found on some dispensers (Universal Instrument AMV for example). These are unique to the application and manufacturer.